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Chemistry Key Concepts: Chapter 8 and 9 - CH 221 Ziegler - Prof. Zelda Ziegler, Study notes of Chemistry

Material Type: Notes; Professor: Ziegler; Class: General Chemistry I; Subject: Chemistry ; University: Central Oregon Community College; Term: Fall 2004;

Typology: Study notes

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CH 221--Ziegler
Chapter 8,9
KEY CONCEPTS
Class period 1 -- Reading pp. 275- 278(t)
1. State the number of valence electrons for a main-group element. Problem 8.1
2. Draw the electron-dot symbol for a main-group element. Problems 8.5, 8.6
3. State the “octet rule.” Problem 8.2
Class period 2 -- Reading pp. 280 – 291
4. Identify periodic trends in electronegativity. Problems 8.33
5. Predict the polarity of a bond. Problem 8.35, 8.36
6. Draw Lewis structures for molecules and polyatomic ions. Problems 8.43, 8.44.
Class period 3 -- Reading pp. 292- 297, 315 – 323; 328 -329 (b)
7. Use calculated Formal Charges to evaluate Lewis structures. Problem 8.46
8. Write resonance forms. Problems 8.47, 8.48 a and b
9. Use the Lewis structure to predict molecular geometry and bond angles. (Note:
you will be required to do this only for molecules and ions in which the octet rule
is satisfied for all atoms.) Problems 9.11 a-d., 9.15, 9.16
10. From the geometry of a polyatomic ion or molecule, predict whether it is polar
or nonpolar. Problems 9.22, 9.25, 9.27.
Class period 4 -- Reading pp. 330 – 334(b), 336 – 339
11. State the hybridization in a covalently bonded species. Problem 9.43
12. State the number of pi and sigma bonds in a molecule or polyatomic ion.
Problems: For the molecules in Problems 9.43, 9.16 and 9.27, state the number
of sigma and pi bonds in each molecule
Answers to Problems:
8.1 See Text A-8
8.2 The octet rule is the observation that atoms will gain lose or share electrons to achieve the
stable configuration of 8 valence electrons. The reason it is in quote marks is that it has so
many exceptions. Specifically, H, He, and pretty much everything in the lower periods.
8.5 See Text A-8.
8.6 a)
M
gii
b)
A
s
••
ii
c)
[]
3
3::
Sc or Sc
+
+
ii
ii
d)
2
::Se
ii
ii
8.33 See Text A-9
8.35 See Text A-9
8.36 NOTE: The answer book refers you
to Figure 8.9 when they mean Fig 8.6
a) O-F < C-F < Be-F
pf2

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CH 221--Ziegler

Chapter 8,

KEY CONCEPTS

Class period 1 -- Reading pp. 275- 278(t)

1. State the number of valence electrons for a main-group element. Problem 8.

2. Draw the electron-dot symbol for a main-group element. Problems 8.5, 8.

3. State the “octet rule.” Problem 8.

Class period 2 -- Reading pp. 280 – 291

4. Identify periodic trends in electronegativity. Problems 8.

5. Predict the polarity of a bond. Problem 8.35, 8.

6. Draw Lewis structures for molecules and polyatomic ions. Problems 8.43, 8.44.

Class period 3 -- Reading pp. 292- 297, 315 – 323; 328 -329 (b)

7. Use calculated Formal Charges to evaluate Lewis structures. Problem 8.

8. Write resonance forms. Problems 8.47, 8.48 a and b

9. Use the Lewis structure to predict molecular geometry and bond angles. (Note:

you will be required to do this only for molecules and ions in which the octet rule

is satisfied for all atoms.) Problems 9.11 a-d., 9.15, 9.

10. From the geometry of a polyatomic ion or molecule, predict whether it is polar

or nonpolar. Problems 9.22, 9.25, 9.27.

Class period 4 -- Reading pp. 330 – 334(b), 336 – 339

11. State the hybridization in a covalently bonded species. Problem 9.

12. State the number of pi and sigma bonds in a molecule or polyatomic ion.

Problems: For the molecules in Problems 9.43, 9.16 and 9.27, state the number

of sigma and pi bonds in each molecule

Answers to Problems: 8.1 See Text A- 8.2 The octet rule is the observation that atoms will gain lose or share electrons to achieve the stable configuration of 8 valence electrons. The reason it is in quote marks is that it has so many exceptions. Specifically, H, He, and pretty much everything in the lower periods. 8.5 See Text A-8.

8.6 a) i M g i

b) As

i i

c) [ ]

3 3

Sc or : Sc :

  • ⎡^ ⎤ ⎢ ⎥ ⎣ ⎦

i i

i i

d)

2

: Se :

− ⎡ ⎤ ⎢ ⎥ ⎣ ⎦

i i

i i

8.33 See Text A- 8.35 See Text A-

8.36 NOTE: The answer book refers you to Figure 8.9 when they mean Fig 8. a) O-F < C-F < Be-F

b) N-Br < P-Br < O-Br c) C-S < N-O < B-F 8.43 See Text A -

8.44 a) H 2 CO

H C H

O

b) H 2 O 2

O O H H

c) C 2 F 6

C C

F F F F

F

F

d) AsO 3 3-

As O O

O

e) H 2 SO 3

H O (^) S (^) O

H

O

f) C 2 H 2 H^ C^ C H

Lewis Structure Formal Charge calculation Oxidation #s a) SO 2

there are 2 resonance forms

O S O

O S O

v.e- 6 6 6 -(e on each atom) 6 5 7 Formal Chg: 0 +1 -

S O

(as per ch 4. )

b)SO 3

There are 3 resonance forms.

O

S O O

O O S O

v.e- 6 6 6 6 -(e on ea. atom) 7 7 4 6 Formal Chg: -1 -1 +2 0

S O

c) SO 3 -

O S O

O 2 -

O O S O

v.e- 6 6 6 6 -(e on ea.atom) 7 7 5 7 Formal Chg: -1 -1 +1 -

S O

d) SO 4 -

O S

O

O

O

2 -

O O S O O

v.e- 6 6 6 6 6 -(e on ea. atom) 7 7 5 7 7 Formal Chg: -1 -1 +2 -1 -

S O

8.48 a) [ :O =N= O: ] +^ ↔ [ --N≡ O: ] +^ ↔ [ : O≡N-- Ö: ] +

b) Yes, resonance structures are needed to describe the structure.

9.22 The 2 polar bonds in H 2 O would completely cancel each other out if the molecule were linear, and then the net dipole moment would be zero. Since water is polar, the molecule can’t be linear.

Key Concept 11 problem sigma bonds pi bonds 9.43 9 1 9.16 a 3 1 b 6 1 c 4 0 d 5 2 9.27 5 1